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This study is concerned with presenting control strategy for interlink converters in hybrid microgrids. When both ac microgrids (AC-MGs) and dc microgrids are in the vicinity of each other, they can be interconnected via ac-dc converters, known as ICs, making it possible to exchange energy between two grids. Common methods employed in IC control strategy use frequency variation and CCM in their structure. This method requires the frequency variation at IC ac-side to be large, leading to poor power quality and stability of AC-MG. Furthermore, CCM does not directly regulate the IC ac-side voltage, which again deteriorates the IC ac-side voltage quality. The proposed strategy is based on droop method, similar to what is used in the autonomous control of sources in an AC-MG. This technique uses voltage-controlled method and does not need frequency measurement in its structure. This considerably improves the voltage quality of AC-MG. The derivation of appropriate droop characteristic is explained. Time-domain simulation is used to verify the performance of the proposed method. The small-signal stability of the system is studied. It is shown how by introducing a proper virtual impedance, the small-signal stability of the system can be improved. [ABSTRACT FROM AUTHOR]

The first part of this article reviews the concepts of apparent power and power factor in single-phase circuits with non-negligible line impedances. The study is based on the well-known definition that the apparent power is the maximum load power subject to constant line losses and constant load voltage. In reality, however, all transmission/distribution lines have some finite impedance, and thus, the constant voltage condition cannot be maintained at the load terminals. In this article, the constant load voltage condition is relaxed and allowed to change, as long as it remains within acceptable range of application. This is a scenario that better reflects the realistic situations. Modified expressions for the apparent power and power factor are derived and discussed. The second part of the article presents a new concept called the current factor as the ratio of the minimal current to the actual current while keeping the load power constant. The current factor coincides with the power factor when the line impedances are neglected. The article explains how the current factor can be superior to the power factor when the line impedances are not negligible. The current factor is then extended to non-sinusoidal current factor for a non-linear load and is examined. [ABSTRACT FROM AUTHOR]